As illustrated in U.S. Pat. No. 4,833,477 issued to Robert K. Tendler and incorporated herein by reference, an emergency vessel location system is described in which, upon activation, latitude and longitude from a navigation unit is decoded and provided in synthesized voice to the modulation section of a transmitter. As a result the transmitter transmits not only the fact of a mayday situation, but also decoded latitude and longitude, all in human synthesized voice. As described in U.S. patent application Ser. No. 08/527,588, the system for modulating the transmitter section of a transceiver includes means for entering a vehicle or a vessel identification number, in one case via a verbal scroll technique. In any event, the emergency message includes not only the mayday indication but also verbalization of an identification number, in this case a vehicle or a vessel identification number, as well as the decoded latitude and longitude.
While the above system was designed to be utilized with a transceiver which broadcasts on a designated emergency frequency or channel, such as channel 16 for VHF radio, channel 9 for citizens' band radio or a frequency of 155.475 MHz for police/EMT emergency purposes, it became apparent that cellular communication systems provided a further opportunity to expand emergency signalling. As is common practice, cellular phones are used to dial 911 in cases of emergency. However, even when 911 is dialed in, it is still difficult to ascertain the location of the cellular phone, either by radio direction finding techniques, or by cellular ranging techniques. As a result, even though the United States Coast Guard has authorized the utilization of *CG to automatically dial a Coast Guard telephone number, it is impossible for the Coast Guard to locate vessels in distress due to the lack of location information on the transmission.
This lack of ability to locate a cellular phone also applies not only to vessels at sea but also to vehicles or persons in distress. Not only do vehicles get into emergency situations in which an airbag is deployed and one tries to dial 911, many have tried to use cellular phones and 911 to foil a hijacking or theft of a vehicle.
In the past, cellular phones have been utilized to digitally signal the location of an emergency situation through a system provided by the Code Alarm company. Such a system utilizes information from a LORAN and causes the cellular phone to dial an 800 number. The cellular phone then transmits digital information concerning vehicle identity and location to a monitoring location. It will be appreciated that specialized demodulation equipment must be provided at the monitoring site to be able to decode the digital information. More importantly, the Code Alarm system requires a specific digital format or sentence structure which is not universally decodeable by others. Thus, implementing such a system requires both specialized demodulation equipment and paid personnel to man the particular telephone number on a 24-hour basis. Such systems are not only costly to implement, but are also costly to the user and usually require monthly user fees.
By way of further background, another type of cellular phone vehicle location system is one in which a ranging system is built into cell site protocols. However, to adequately cover a city, approximately 10 cell sites all equipped with the ranging programs must be in place. While this system operates to identify and locate a vehicle in distress, it is even more expensive to man and operate than the Code Alarm system due to the initial cost of the ranging programming, to say nothing of the additional towers necessary.